Rotary Swap Miata (Not the CJ Wilson car)

Sooo, the belt drive thing... I am not sure why in THIS application.

Most people who race their rotary and zing it up pretty good will at some point have belt troubles. This is the nuke option to solve that.

MOST people have water pump issues with the stock belts. The belt only contacts the water pump about 65 Deg around the pulley. Not much contact. So, the solution is to run 2 belts and get a 2 belt pulley for the alt. This works... Mostly. It can still lead to cavitation of the waterpump AND the belts are NEVER the same length (even "matched ones").

Eventually, you get fed up and run the gilmore drive.

Back to this car.... I have no idea why. The water pump is not there. This is simply the eccentric shaft runnign the alternator.

This was an option once upon a time: http://lucky7racing.net/collections/featured/products/miata-13b-rotary-mount-kit

The exhaust on the same side as the ppf is also an issue.

Swank Force One wrote: 2) Any reports of anyone successfully using a Miata 6spd on a 13B?

A friend who has access to Mazda parts books and stuff says that the Miata 6sp stuff is all smoothcase (N/A RX-7) sized input and output shafts, while RX-8 6sp is all ribcase (Turbo RX-7) sized input and output, and it is indeterminate if you can stick an RX-8 front transmission chunk on a Miata/MX-5 transmission like you can with Miata 5-speed and RX-7 smoothcase bits.

When we was lookin' at EvanB's empty engine bay, my gut feeling was that the best way to package the exhaust is to just sacrifice the passenger footwell a bit and have the exhaust run out that way for a bit.

Swank Force One wrote: That IS fuel injected? Well that's fun.

Looks like the throttle body setup that Anniversary Racing Factory uses.

https://www.youtube.com/watch?v=up_O2unwbro

You... may want to check out that guy's other videos. Lots of RX-7 and Miata content. They do a lot of N/A conversions to FCs and FDs, sometimes with EFI sometimes with Weber IDAs, sometimes stock ports sometimes peripheral, also plenty of ITBs on B6 engines...

alfadriver wrote: Although, I can't really see the reason why one would use a timing belt to just turn the alternator. Plenty of wide grooved belts to use.

There's kind of a fetish for cogged belts in the rotary community. Besides making a cool whine like a geardrive, Mazda laid out the accessories so that the alternator belt only barely glances off of the water pump pulley on the SLACK slide. The air pump pulley (when present...) is what mainly drives the water pump and fan. Eliminate the air pump and the belt slips a LOT. Eliminate the clutch fan and the slippage doesn't get so bad but it does still happen at high RPM when the pump goes into cavitation.

So the fix is a cogged belt so the water pump pulley never slips. Which, as you note, makes no sense when you have an ELECTRIC water pump and have completely eliminated the water pump/thermostat housing.

wvumtnbkr wrote: So, the solution is to run 2 belts and get a 2 belt pulley for the alt. This works... Mostly. It can still lead to cavitation of the waterpump AND the belts are NEVER the same length (even "matched ones"). Eventually, you get fed up and run the gilmore drive.

I think you may have had some wires crossed. Cavitation is when the water pump's impellers are moving so far out of their efficiency range that the water cavitates - the low pressure area behind the impellers gets SO low that it creates vacuum or vapor and water flow drops and becomes unstable. Mazda OEM pulley/pump arrangements generally go into cavitation at about 6000 rpm. Racing Beat has some charts that break it down by pump and pulley combo, but they all cavitate at remarkably low RPM. Double belts band-aid the slippage problem but they do not solve the underlying problem of the water pump simply spinning too fast to be able to pump coolant effectively.

At one point I was eating one belt per month from slippage. Then I installed a 3.5" crank pulley. Thus both increased belt wrap but more importantly brought the water pump speed down into a range where it always pumped smoothly. Belt life is now up to "I put a belt on in 2012 and it's still good".

The Gilmer drives do sound sweet, I'll admit. And they are fine on street cruisers and turbo cars. But they all spin the water pump too fast for extended N/A performance use, just like the stock belt drives.

Knurled wrote:

wvumtnbkr wrote: So, the solution is to run 2 belts and get a 2 belt pulley for the alt. This works... Mostly. It can still lead to cavitation of the waterpump AND the belts are NEVER the same length (even "matched ones"). Eventually, you get fed up and run the gilmore drive.

I think you may have had some wires crossed. Cavitation is when the water pump's impellers are moving so far out of their efficiency range that the water cavitates - the low pressure area behind the impellers gets SO low that it creates vacuum or vapor and water flow drops and becomes unstable. Mazda OEM pulley/pump arrangements generally go into cavitation at about 6000 rpm. Racing Beat has some charts that break it down by pump and pulley combo, but they all cavitate at remarkably low RPM. Double belts band-aid the slippage problem but they do not solve the underlying problem of the water pump simply spinning too fast to be able to pump coolant effectively. At one point I was eating one belt per month from slippage. Then I installed a 3.5" crank pulley. Thus both increased belt wrap but more importantly brought the water pump speed down into a range where it always pumped smoothly. Belt life is now up to "I put a belt on in 2012 and it's still good". The Gilmer drives do sound sweet, I'll admit. And they are fine on street cruisers and turbo cars. But they all spin the water pump too fast for extended N/A performance use, just like the stock belt drives.

You are correct sir. Slippage is the main concern for most people. Thanks!

Knurled wrote: There's kind of a fetish for cogged belts in the rotary community. Besides making a cool whine like a geardrive...

LOL- I thought one of the features of the roatary WAS it's sound- and they think they need to add MORE?

One ear bleeding just isn't enough...

In reply to alfadriver:

Could be worse, could have a straight cut trans in there to boot.

https://www.youtube.com/watch?v=mZPwjvuQzhM

Hell why not. This is the same forum that had a thread that was basically "Crashbox? Sounds pleasant! Why not put them in EVERYTHING!".

I looooooove that car.

But... With how slow he was going, why couldn't he stay in his lane?

Vigo wrote: Hell why not. This is the same forum that had a thread that was basically "Crashbox? Sounds pleasant! Why not put them in EVERYTHING!".

I said straight cut, not crashbox :)

Although crashbox might technically be different from dogbox... both are unsynchronized but IIRC chrashbox specifically means a setup where you physically slide a gear in and out of mesh.

Car I like better than Logan's (because two rotor, and 1st-gen)

https://www.youtube.com/watch?v=WX0IkVMIHsA

Knurled wrote: In reply to alfadriver: Could be worse, could have a straight cut trans in there to boot. https://www.youtube.com/watch?v=mZPwjvuQzhM

It's saying something when the trans is louder than the rotary engine.

Which I translate as "I'm CHOKING on too much muffler!"

Seems like what I heard over that trans.

Good think that the passenger took a bumpy hand held video, with that nice camera in the cage. Could have enjoyed the ride instead....

In reply to alfadriver:

He was pushing close to 500whp with a non turbo three rotor... Defined is known for their highly, highly efficient exhaust systems.

My car is probably louder, and makes a third the horsepower

Swank Force One wrote: I'm half-contemplating attempting this on my 2000 SE, for no good reason other than i think it would be cool, and i'm not limited by any rules for this car. Questions: 1) Anyone have a link to a good build thread with lots of pictures? 2) Any reports of anyone successfully using a Miata 6spd on a 13B? This is what i have in mind, but with 100% more fuel injection.

Berking Swank, now I want to build a rotary miata.

Anyone else noticing that this thing is rhd?

I like the open engine bay above but still have 0 want for a rotary anything....sorry but I'm allowed my opinions.

In reply to sesto elemento:

Yes, makes the column deal less of a problem i believe.

In reply to Swank Force One:

RHD makes rotary more difficult, not less. The steering and the exhaust want to be in the same spot.

This is why RX-7s have the engine cocked way over to the left side of the car.

my buddy erik did one.....

I say do it. Yeah, he would wouldn't he?

I just looked at the RX8 6 speed trans in my garage, it has the PPF mounts on the left side. It might take perhaps melding an RX8 and a Miata PPF but I bet that's doable. That also frees up right side space for the exhaust.

On belts: I'm running dual belts on my 13BT for the reasons listed. It still can have the problem of the belts 'growing' away from the water pump pulley at very high RPM, in fact the CW in the rotary community is that Mazda put 7500 RPM buzzers on first gens and RPM limiters on later ones not because of anything in the engine but so it wouldn't fling belts.

I'm considering moving the alternator down to the left side of the engine, then run dual belts for the water pump the same way the circle track guys do on small block Chevys, then run a single belt from the e shaft to the alternator.

Water pump drive:

I can replicate this pretty easily by just buying two belts short enough to go around the stock E shaft and water pump pulleys. The alternator drive pulley would be one of the pulleys which bolt to the E shaft in front of the water pump drive. For that matter, I could also run it off the front of the water pump but would have more crank angle sensor clearance if I run it off the E shaft. Installing the water pump belts is pretty easy; first be sure you use studs and nuts to hold the pulley on. Take the nuts off, this allows the pulley to lean at a considerable angle. Install the belts, then reinstall the nuts to pull the belts tight.

Seems like an electric pump is the way to go huh?

Does an rx8 diff bolt into a Miata? Rx8 trans and diff combo moves the PPF out of the way of the exhaust. If you need to shorten the PPF I think the middle has the longest consistent portion that would be easy to chop.

RX8 differential:

Late Miata differential:

The Miata mount is part of the diff rear cover. If that will bolt to the RX8 diff, damn it's easy. If not, then that means fabricating a mount. Not insurmountable.

I think the late Miata inner CV will go directly into a RX8 diff, but I don't know for sure. If it will then the whole thing is pretty simple. From what I've been able to find, the FD RX7 and 929 share the diff with the RX8 and there's talk (unproven) that they can be installed easily in a Miata. EDIT: According to solomiata, no an FD diff (and thus an RX8) is not a bolt in for a Miata. http://www.solomiata.com/Drivetrain.html

Here's a pic of an 8.8 Ford modified to fit in a 2nd gen RX7 which has a diff mounting very similar to a Miata. I would think something similar could be fabbed for an RX8 diff.

sesto elemento wrote: Seems like an electric pump is the way to go huh?

The answer: it depends. I don't particularly care for electric water pumps on a street car. Too much to go wrong. Now, on a race car yes very possible. And no I have not ruled it out for my car; I'm wanting to slow down the water pump so if I can do that with a smaller E shaft pulley or a larger water pump pulley and still have it engine driven it does remove one possible break point.